Project Summary/Abstract Colorectal cancer (CRC) is among the leading types of cancer in men and women. One of the processes commonly dysregulated in cancer is proteolysis: key proteases play pro-oncogenic roles, often in a tissue-specific manner. Consequently, identifying and characterizing proteases critical for oncogenesis provides new opportunities to combat cancer. Through in silico and histological analysis, we identified TMPRSS13 to be markedly upregulated in CRC. TMPRSS13 is a Type II Transmembrane Serine Protease that is largely uncharacterized, with no physiological substrates identified and no cancer-related findings reported thus far. Preliminary work suggests that siRNA-mediated silencing of TMPRSS13 impairs cellular proliferation, and promotes apoptosis. Importantly, TMPRSS13 leads to a decrease in expression of claudin-2, a tight junction protein that has been implicated in increased CRC tumorigenicity and resistance to the chemotherapeutic agent 5-FU. We hypothesize that TMPRSS13 promotes cancer cell survival and CRC progression via regulation of the tight junction protein claudin-2. To test this hypothesis and to pinpoint the molecular mechanisms underlying the function of TMPRSS13 in CRC, in vitro and in vivo studies will be conducted. I will build upon my preliminary findings using various CRC cell lines to determine how TMPRSS13 regulates claudin-2 to aid pro-oncogenic processes such as proliferation, invasion, and escape from apoptosis. Mechanistic data describing the role of TMPRSS13 on claudin-2 and CRC from cell culture models will be complemented by in vivo studies, where I will use a chemically induced model of colon cancer in TMPRSS13 knockout mice to assess the impact of TMPRSS13 on colon tumor growth and progression in vivo and ex vivo. Collectively, these experiments will provide mechanistic information regarding the steps regulated by TMPRSS13 in CRC development and progression. In characterizing TMPRSS13 as a mediator of CRC, our proposed work will provide novel insight into a potential cancer-specific drug target for CRC therapy.